1. Technical Field
The present disclosure relates to a display device and an illumination device.
2. Description of the Related Art
A display device using a polymer dispersion type liquid crystal panel as a light guide plate of backlight has been known (refer to Japanese Patent Application Laid-open Publication No. 2011-222199). A light source is disposed on an end face of the polymer dispersion type liquid crystal panel. Illumination light emitted from the light source propagates through the polymer dispersion type liquid crystal panel and is emitted from the polymer dispersion type liquid crystal panel. The polymer dispersion type liquid crystal panel is arranged to be opposed to a display panel. The display panel modulates the illumination light emitted from the polymer dispersion type liquid crystal panel and displays an image.
The polymer dispersion type liquid crystal panel includes two substrates including transparent electrodes and a liquid crystal layer sandwiched between the two substrates. Orientation of the liquid crystal layer is controlled by applying a voltage between a pair of electrodes respectively provided on the two substrates. The illumination light propagates through the polymer dispersion type liquid crystal panel while transmitting through the liquid crystal layer and the electrodes.
The polymer dispersion type liquid crystal panel includes a plurality of sub illumination regions, in which, switching between a scattering state where the illumination light is scattered and a non-scattering state where the illumination light is not scattered, are independently controlled. A light quantity of the illumination light to be emitted from each sub illumination region is controlled according to the time for applying the voltage to the liquid crystal layer in each sub illumination region. A drive system of this kind of backlight includes static drive for collectively lighting all the sub illumination regions and scan drive for sequentially lighting the plurality of sub illumination regions. However, it is not easy to accurately control the light quantity of the illumination light to be emitted from the sub illumination region.
For example, the plurality of sub illumination regions are aligned from a side close to the light source to a side far from the light source. When the static drive is performed, since all the sub illumination regions are in the scattering state, a large amount of the illumination light is scattered in the sub illumination region close to the light source, and the light quantity of the illumination light which reaches the sub illumination region far from the light source is reduced. Therefore, in the sub illumination region close to the light source, the time for applying the voltage to the liquid crystal layer is set to be short. In the sub illumination region far from the light source, the time for applying the voltage to the liquid crystal layer is set to be long. However, with this method, there is a possibility that sticking unevenness is generated between the sub illumination regions due to the difference between the times for applying the voltage to the liquid crystal layer. Therefore, it is necessary to perform the drive with an effort to prevent the sticking unevenness.
When the scan drive is performed, the sub illumination regions to be in the scattering state are switched for each divided period in which a unit period (for example, a single frame period) is divided into the number of sub illumination regions. The light quantity of the illumination light to be emitted from the sub illumination region is set according to brightness of the image to be displayed. Therefore, when a dark image is displayed, the time for applying the voltage to the liquid crystal layer is reduced. However, when the time for applying the voltage is more reduced within the originally short divided period, there is a possibility that the response of the liquid crystal layer is insufficient and the target light quantity cannot be obtained.